Description

This short example will utilize GNU Radio benchmarks scripts to transfer packets over a radio link between two nodes.

Hardware / Software Resources utilized

Grid nodes with a USRP2 connect via Ethernet.

baseline-sdr.ndz: disk image loaded onto nodes. This image has all the precompiled - software required to configure the USRP2s and all the required GNU Radio software libraries. The USRP2's interface with the node is already configured.

Login into reserved domain: ssh username@grid.orbit-lab.org

Login into reserved domain

During your approved time slot, you will be able to ssh into the console of the respective domain. A console is a dedicated machine that allows access to all resources in that domain.

For example, to access the sandbox1:

yourhost>ssh username@console.sb1.orbit-lab.org
Using username "username".
Authenticating with public key "xxxxxxxxx"
Welcome to Ubuntu 12.04.1 LTS (GNU/Linux 3.2.0-36-generic x86_64)
* Documentation: https://help.ubuntu.com/
System information as of Mon Jan 28 20:25:50 EST 2013
System load: 0.0 Processes: 93
Usage of /: 2.7% of 69.43GB Users logged in: 0
Memory usage: 6% IP address for eth0: 10.50.18.10
Swap usage: 0% IP address for eth1: 10.18.0.10
Graph this data and manage this system at https://landscape.canonical.com/
9 packages can be updated.
0 updates are security updates.
|-----------------------------------------------------------------|
| *** For authorized use only *** |
| This system is for the use of authorized users only. All users |
| are expected to comply with the "Acceptable Use Policy" availa- |
| ble at http://www.orbit-lab.org/AUP.html |
| Individuals using this computer system, are subject to having |
| all of their activities on this system monitored and recorded |
| by system personnel. |
| |
| Anyone using this system expressly consents to such monitoring |
| and is advised that if such monitoring reveals possible |
| evidence of criminal activity, system personnel may provide the |
| evidence of such monitoring to law enforcement officials. |
| |
| Email question, comments or problems to help@orbit-lab.org |
|-----------------------------------------------------------------|
username@console.sb1:~$

Individual nodes are identified in the output of stat command by their fully qualified domain name (FQDN). This establishes their "coordinates" and the "domain" to which they belong. Nodes in different domains typically can NOT see each other. Node can be in 1 of 3 states:

Two important arguments are TOPOLOGY describing the set of nodes one wishes to image , and !IMAGE specifying the name of the image one wants to load the nodes with. If the imaging process does not does not finish within the default timeout period, that period can be increase by using the -o flag (e.g. -o 1600).
Typical command to load both nodes of sandbox 1 with the baseline? image would look like:

If the node is in the NOT REGISTERED state, you may need to wait for it to recover the POWEROFF state (it some times requires a few moments for the services to sync up). If the node takes more than 60 seconds to come out of the NODE NOT AVAILABLE state please report it to an administrator.

Troubleshooting

If the receiving script is not showing any activity, it most likely the script parameters need to be tweaked. USRP radios (any radio in general) are not made the same due to variations in HW component quality and tolerances. Each radio has it's own sweet spot for best transmission and reception. For different USRPs on the grid (or other sandboxes) raising or lowering gains, amplitude, and/or other parameters is required to establish a solid radio link.

As an example if the gains are set too hi, signal can become saturated, clipped and distort at the analog-digital interface. If the gains are set too low, the signal will just blend in to the noise floor especially for simple modulation schemes. For a description of other parameters, use the —help command get a listing.